Two-Part Pterional CraniotomySharon Devasagayam , Arnau Benet , Michael W. McDermott
1. Department of Neurological Surgery, University of California, San Francisco 2. UCSF Dept ofNeurosurgery, UCSF Dept of Otolaryngology - Head and Neck Surgery 3. Neurological Surgery,University of California San Francisco, San Francisco, USA
AbstractIntroduction: The standard approach for pterional craniotomy involves one or two burr holesand a single bone piece encompassing the frontal, temporal and sphenoid bones. Drilling downof the sphenoid creates a defect that requires repair. We have used a two-part pterionalcraniotomy that avoids the need for drilling and document the modification of the standardtechnique here.
Methods: Two burr holes are placed, one behind the key point over the frontal fossa as well asone on the temporal fossa. A frontal temporal sphenoidal bone flap is created by cutting thebone back in a V-shape around the sphenoid wing. Extradural dissection is then done to exposethe lateral part of the sphenoid wing down to the dural fold lateral to the superior orbitalfissure, as well as separating the dura from the floors of the anterior and middle cranial fossa. Afoot plate attachment on the drill is used to create a secondary bone piece which encompassesthat portion of the greater sphenoid wing that is drilled away in the standard approach.Reconstruction is done connecting the two pieces back together with titanium plates andscrews yielding a good cosmetic result.
Conclusions: A two part pterional craniotomy is an option for a standard frontal temporalsphenoidal approach that allows for preservation of bone and assists with reconstruction andmay provide for a better cosmetic result.
IntroductionThe standard approach for access to the frontal, temporal, sphenoid wing, supra-sellar regions,as well as the anterior and middle cranial fossa, can be done with a classically describedpterional approach [1-5]. This begins with a burr hole at the key point, which is actually at thejunction of the anterior inferior part of the anterior cranial fossa, the orbit and greatersphenoid wing. Frequently orbital contents are entered with placement of this hole. Once apterional craniotomy is done, access to deeper portions of the anterior and middle cranial fossais gained by drilling down the greater sphenoid wing. This creates a bony defect which must berepaired in order to achieve a good cosmetic result for the patient [6-11].
We have used a two-part pterional craniotomy recently to assist us with ease of opening andachieving a better cosmetic result but not requiring longer operative time. The first burr hole isplaced behind the standard key hole more towards the anterior cranial fossa below the standardtemporalis muscle cuff and the second one in the temporal fossa posteriorly. The shape of thefirst bone flap is not the customary approach because it preserves the lateral part of the
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Open Access TechnicalReport DOI: 10.7759/cureus.69
How to cite this articleDevasagayam S, Benet A, Mcdermott M W. (November 24, 2012) Two-Part Pterional Craniotomy. Cureus4(11): e69. DOI 10.7759/cureus.69
sphenoid wing by cutting a V-shape around it, which is then dissected secondarily under directobservation and removed with the foot plate attachment up to the region of the key point.
Technical ReportThe standard patient positioning is used and 3-point fixation. Once the skin flap is turned downto expose the skull and temporalis muscle the muscle is reflected down of the frontal temporaland sphenoid bones leaving a cuff of muscle to suture the muscle back to at the end of theprocedure.
With this region of the skull sufficiently exposed, we use two, rather than the classicallydescribed four, burr holes technique of Yasagril (Figures 1-2) [1-2]. The first burr hole is placedbehind the standard key point, and a second is located posteriorly in the temporal bone(Figures 3-4). The drill is used to cut between the burr holes so as to exposure the dura of thefrontal and temporal lobes by creating a frontal temporal sphenoid bone flap (Figures 5-6). Thisbone flap preserves the lateral wing of the sphenoid, unlike the drilling of the standardapproach, and this region of bone is removed with the use of a foot plate attachment(Figures 7-11).
FIGURE 1: Bone exposure below muscle outlining two partcraniotomy outlining position of burr holes and cut lines in
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FIGURE 2: Surgical simulation photographs illustrating theposition of the two-part pterional craniotomy.A: Right pterional approach. After a wide skin flap, the temporal fascia was carefully dissected topreserve both facial and supraorbital nerves. The temporal muscle was incised 1 cm from itsattachment along the superior temporal line to leave a muscle cuff in order to ease closure andoptimize postoperative muscle function. The first part pterional craniotomy (Green) was performedfirst. Then, the complimentary second part sphenoidal craniotomy (Orange) is removed using footplate under direct view.
B: Detail of the right classic McCarty Keyhole and relative position of the frontal burr hole for thetwo-part pterional craniotomy. The McCarty Keyhole has been performed to show the limit betweenthe orbital and intracranial compartments. The exocranial facet of the sphenoid bone has beenidentified (Dotted line) and the frontal (White circle number one) and temporal (White circle numbertwo) burr holes have been identified.
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FIGURE 3: Frontal burr hole and second burr hole positions.Frontal burr hole for anterior fossa is behind standard standard key-hole. Second burr holeposteriorly in squamous temporal bone.
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FIGURE 4: Skull photographs illustrating the two-piecepterional craniotomy.A: Left exocranial view of the skull showing the modified bone flaps in the two part pterionalcraniotomy. First part (green) and the second part craniotomy (Orange).
B: Right endocranial view of the skull showing the relation of the craniotomy sub-parts to the petroustemporal bone, lesser sphenoid wing and orbit. The modified Keyhole (Green circle) is placedposterior and superior to the classic pterional keyhole. LWSB: Lesser Wing of the Sphenoid Bone
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FIGURE 5: Recommended sequence of cuts with footplate.(1) begin in temporal burr hole and cut in curvilinear fashion to supra-orbital margin, then back out.
(2) From frontal burr hole cut forward towards keyhole and then turn up towards supra-orbitalmargin, pivoting drill so footplate does not hang up on inner table of frontal bone above roof of orbit.
(3) From frontal burr hole cut posteriorly around back edge of sphenoid wing, then forward belowwing into middle fossa turning back at end into temporal burr hole.
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FIGURE 7: Extradural dissection begins over roof of orbitworking backwards to sphenoid wing.Once wing identified dura dissected off to dural fold over lateral aspect of superior orbital fissure.Then dura below wing to anterior limits of middle fossa dissected.
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FIGURE 10: Once footplate passes the sphenoid ridge drill isturned anteriorly and cut is directed parallel to roof of orbitdirectly towards keypoint (7).
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FIGURE 11: Final exposure after second part pterionalcraniotomy that has not required any drilling of lateralsphenoid wing.
The dura can be opened in a semi-lunar fashion and reflected back to maximize corticalexposure as necessary. At the end of the procedure, standard cranial reconstruction usingtitanium plates and screws is undertaken, followed by normal closure of the retractedsuperficial tissue. This technique does not increase surgical time, but results in a superiorreconstructive and thus cosmetic result. A cadaver video dissection with audio can be seenfollowing the link: http://www.youtube.com/watch?v=qyG4UF3XdBk
DiscussionThe pterional craniotomy ("frontotemporosphenoid") is the term given to an approach which isfocused on the junction of the frontal, temporal, parietal, and sphenoid bones [1-5]. Thisparticular craniotomy has become one of the most dominant approaches amongstneurosurgeons by virtue of its extreme versatility and proven utility.
The pterional craniotomy evolved from the frontolateral craniotomy described by Dandy, whichwas originally created to expose the optic chiasm and pituitary. The now "classical" pterional
approach was popularized by Yasagril in the second half of the 20th century [1-2].
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Modifications have continued to arise, and the beauty of the pterional approach has been thatit is a procedure adept at managing a large spectrum of disorders ranging from neoplasticpathologies to vascular lesions arising anywhere on the circle of Willis [12-16]. A neurosurgeonis able to address lesions via this technique that are in the sella and parasellar regions, as wellas subfrontal, frontolateral and temporal areas. As required by the scenario at hand, thepterional approach elegantly provides access to the optic nerves, chiasm, lamina terminalis,cavernous sinus, as well as the circle of Willis. Further testament to its versatility is howcommonly and easily it can be combined with other approaches. Nowhere is this highlightedbetter, than the orbitozygomatic approach, which at its core is essentially the original pterionalapproach proposed by Yasagril. The difficulty for the surgeon is crossing the sphenoid wing withthe drill. This can usually not be done with a footplate attachment and other methods, such asdrilling a trough across the wing or simply fracturing it open, are commonly used. Once the freebone flap is removed, the bone of the lateral wing is usually drilled down to expose the orbito-cranial periosteal fold to assist with better medial intradural exposure. Reconstruction of thisbony defect is required at closure to provide a good cosmetic result and avoid a temporalhollow. The two part pterional technique avoids the difficulty of free bone flap by allowingdirect exposure and sub-periosteal dissection of the sphenoid wing prior to removal in thesecond step of the procedure. The second bone piece is removed using the footplate underdirect vision using the medial orbito-cranial periosteal fold as the medial landmark for crossingthe wing with the footplate. At closure, no reconstruction is required other than connecting thebone pieces together with plates and screws.
The so-called mini-pterional craniotomy, like the tranciliary orbital keyhole technique, is aimedat providing an alternative to the pterional approach [13, 16]. This procedure has been shown togive exposure comparable to the classical pterional approach for much of the anteriorcirculation, while at the same time reducing the extent of dissection of the temporalis muscle.However, the pterional approach still affords the neurosurgeon greater exposure of thetemporal lobe, better exposure of the MCA branches, and furthermore, allows a greaterflexibility by facilitating a more anterior approach than possible with the mini-pterional. Lastly,this technique continues to also drill down the sphenoid bone, something unnecessary in ourapproach, and which has the potential to compromise the bony support and thus cosmeticoutcome for the patient.
ConclusionsThe two part pterional approach is an option to the classic technique and has severaladvantages for the surgeon and patient. For the surgeon the technique may be easier in that itavoids the difficulty with crossing the sphenoid wing and may eliminate the need forreconstruction with titanium mesh or other impants at closure. For the patient, improvedcosmesis may result from preservation of the sphenoid bone supporting the temporalis muscle,avoiding the depression just behind the orbit.
Additional InformationDisclosuresHuman subjects: All authors have confirmed that this study did not involve humanparticipants or tissue. Animal subjects: All authors have confirmed that this study did notinvolve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniformdisclosure form, all authors declare the following: Payment/services info: All authors havedeclared that no financial support was received from any organization for the submitted work.Financial relationships: All authors have declared that they have no financial relationships atpresent or within the previous three years with any organizations that might have an interest inthe submitted work. Other relationships: All authors have declared that there are no otherrelationships or activities that could appear to have influenced the submitted work.
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